DULUTH, Minn. — Humans were the most frequent cause of death for research wolves that live in five of the nation's most highly protected places, national parks, and those deaths led to long-term consequences for wolf packs, a new study has discovered.
Some 36% of collared wolves in the five parks included in the study died at the hands of humans, usually when they ventured just outside the park boundaries and were shot.
The research shows that many wolves that spend most of their time in national parks, like Voyageurs in Minnesota and Yellowstone in Wyoming, still amble out of the park frequently, where they are vulnerable to human-caused deaths, often illegal poaching and, where allowed in some states, legal hunting.
"In all the years of our study, we've never had a single wolf that remained entirely within the park for an entire year," said Thomas Gable, lead scientist in the Voyageurs Wolf Project and a University of Minnesota researcher.
Researchers said those wolf deaths caused instability and long-term repercussions for the wolf packs involved, setting in motion changes that impact whether the pack survives and if new pups are reproduced.
The study was published Tuesday in the journal Frontiers in Ecology and the Environment and included scientists in several states who used data from 193 wolf packs from the five parks and recorded 978 wolf mortalities from 1986-2021.
While past studies already have documented how humans impact wolf populations, this study took a new approach, looking at how human-caused mortality affects individual wolf packs. To do this, Kira Cassidy, a research associate at Yellowstone National Park, and the other scientists contrasted what happened to wolf packs after at least one pack member was killed by humans with packs that had no members that died of human causes.
The researchers found that the odds of a pack staying together to the end of the year decreased by 27% when a pack member died of human causes, and whether or not that pack produced pups the next year decreased by 22%. When a pack leader died, the impact was more substantial, with the chance of the pack making it to the end of the year decreasing by 73% and reproduction by 49%.
"These results indicate that human activities (outside the parks) can have major negative effects on the biological processes of wildlife that use protected areas," the study concluded.
The study looked at wolf deaths from Voyageurs and Yellowstone as well as Denali National Park in Alaska, Grand Tetons National Park in Wyoming and the Yukon-Charley Rivers National Preserve in Alaska.
"For gray wolves, the biological unit is the pack or the family. We wanted to focus on the impacts of human-caused mortality to the pack, a finer-scale measure than population size or growth rate," Cassidy said in releasing the findings.
While the human-caused deaths may not impact the overall population of wolves in each park studied, as other packs may expand to fill in for the affected pack, the study shows that people are clearly altering certain aspects of wolf ecology in national parks.
Of the five parks in the study, wolves in Voyageurs National Park spent the most time outside of park boundaries. In fact, wolves that had territories in or overlapping Voyageurs spent 46% of their time outside of the park. The result: 50% of all mortalities for these wolves came at the hands of people. The largest source of wolf mortality was illegal shooting and at least one wolf studied inside the park was killed by federal trappers when it roamed near a cattle farm outside the park.
"The unique shape of Voyageurs means that there are very few wolf packs that live entirely within the boundaries of the park. Instead, many wolf pack territories straddle the park border and when wolves leave the park, they are at an increased risk of being killed by people," Gable said.
While Voyageurs saw the highest human-caused mortality, the Minnesota park wasn't alone. Human-caused mortality accounted for 36% of collared wolf mortality across all five parks. Legal hunting and trapping of wolves outside of national park boundaries, in places like Alaska, Wyoming and Montana (and Minnesota from 2012-2014, before the animals received renewed federal protections), accounted for 53% of all human-caused mortality for wolves from national parks during hunting and trapping seasons.
"Wildlife populations that cross hard boundaries from federal to state ownership are a challenge to manage. Wolves don't know the park boundary lines," said Joseph Bump, an associate professor in the University of Minnesota's College of Food, Agricultural and Natural Resource Sciences.
"Like other national parks, Voyageurs National Park is managed to minimize impacts on natural ecosystems and natural processes, and wolves are part and parcel of the natural fabric of the park. We will use this information about human-caused mortality of wolves to better inform future management decisions in the park in fulfillment of the NPS mission," said Steve Windels, National Park Service biologist at Voyageurs and a co-author in the study. "More than 50 years of research on wolves in North America has shown wolves to be pretty resilient at the population level. Where this study differs is that we looked at how human-caused mortality affects individual packs of wolves that live mostly in parks. Wolf packs experiencing human-caused mortalities were less likely to persist and reproduce. However, our results show that wolf packs can be resilient to human-caused mortalities even at the pack-level, especially if the pack is large."
Researchers said they hoped the findings might lead to better cooperation between federal agencies in charge of protecting wolves in parks and those state and federal agencies inclined or required to allow wolf killing just outside the parks at the behest of farmers, ranchers and politicians.
"Rather than viewing this result as a failing, we hope this work encourages a renewed interest in interagency collaboration, where management of gray wolves is defined by compromise and based on science, including weighted space-use and cause-specific mortality data," researchers noted in the study's conclusion. "If efforts are made toward this goal, these protected areas and the partners involved can serve as a model for successful transboundary issues worldwide."
Wolves are protected under the federal Endangered Species Act across the western Great Lakes. In Minnesota they are listed as threatened, which allows limited trapping and killing by government trappers but no general public hunting or trapping seasons.
